Field emission devices are well known in the art. Field emission devices generate electron beams from electron emitters at a cathode plate. Each of the electron beams is received at a "spot" on an anode plate and defines a corresponding "spot size." The separation distance between the cathode plate and the anode plate determine, in part, the spot size. It is known in the art to control the spot size by using focusing structures to collimate the electron beams.
High-voltage field emission devices operate at an anode voltage of greater than about 4000 volts relative to the cathode voltage. In these high-voltage devices, the separation distance between the cathode plate and the anode plate must be great enough to prevent unwanted electrical events, such as arcing between the cathode plate and the anode plate. The separation distance that is sufficient to prevent unwanted electrical events can result in an undesirably large spot size. Thus, focusing structures are frequently employed in high-voltage field emission devices.
However, prior art focusing structures often employ dielectric layers to support a focusing electrode and to separate the focusing electrode from the other electrodes, such as gate extraction electrodes, of the field emission device. Furthermore, these supporting dielectric layers determine the distance between the focusing electrode and the other device electrodes.
Such prior art focusing structures suffer from disadvantages. For example, the capacitance between the focusing structures and the gate extraction electrodes increases the power requirements of the device. Furthermore, the presence of the additional support layer increases the risk of generating gaseous contaminants. That is, contaminants can be evolved from the support layer. Generation of gaseous contaminants can occur during any high-temperature condition, such as typically encountered during the final sealing steps in the fabrication of the device.
Accordingly, there exists a need for a field emission device having a focusing structure, which improves operating power requirements and improves contaminant levels over the prior art, while allowing small "spot size" required for high-resolution displays.